Inception is a complex sci-fi thriller that lies somewhere between a James Bond film and The Matrix. We've assembled a spoiler-free guide to the science of the movie, and all you need to know about dreams and the unconscious mind.

In Inception, Dom Cobb (Leonardo DiCaprio) is a dream snatcher. He's an industrial spy, who steals secrets when his victims are at their most defenceless: when they are asleep, and dreaming. But he has an even rarer ability, that of inception. He can plant an idea in someone's sleeping mind, and watch it grow and take root in reality. "The most resilient parasite is an idea," he says.

Is it possible to directly access someone's dreaming mind?

In the movie, the dream-snatchers use a drug called somnacin and a dream machine to upload a scenario into someone's sleeping mind. One or more of them then go to sleep themselves, hooked up to the machine, and enter the target's dream.

A device does already exist that can effectively read someone's mind. A functional MRI scanner takes snapshots of brain activity, and then the software recreates images of what the subject was looking at.

The researchers say it has the potential one day be able to record someone's dream - without the mess and danger (or the fun) of actually sharing that dream.

The dream team of Inception is highly trained at this, which may be why they are able to perform complex tasks - such as reading - which most normal lucid dreamers find difficult. Some of the characters in the movie have also militarised their dreamscapes, to protect themselves against the invasive dream snatchers.

Do dreams have to obey the laws of physics?

This is a fondly debated topic, and Inception has it both ways. Sometimes impossible things happen - in one dream Paris gets folded like a huge sheet of paper - and optical illusions become "real". The endless staircases created by M. C. Escher, for example, exist in Inception dreams thanks to a manipulation something like that occurring in 3D virtual environments.

Without sensory input, consciousness appears to behave in predictable ways. Informal laws can be deduced, for example, the "law of self-fulfilling expectations" (what you expect to happen will happen), the "law of narrative momentum" (linger too long in one place and the dream world begins to fray.

In Inception, the dream world "frays" when external influences from the real world intrude.

How does subjective time pass in a dream?

In Inception, dream time runs much slower than real time, and there is a scaling effect, such that if you dream within a dream, time passes even more slowly. So 5 minutes of real time equals 1 hour of dream time, a 5-minute dream inside a dream equals one week of real time, and so on.